Slip spline assemblies are used in heavy duty applications to transmit torque while allowing for axial translation between input and output components. A conventional slip spline assembly includes a slip yoke having a central longitudinal bore that receives a splined portion of a connection shaft. The internal splines of the yoke bore interfit with the splines of the shaft to provide for torque transfer between the yoke and the shaft while allowing for axial movement between the shaft and the yoke. Lubricant such as grease or other viscous fluid is often used and retained in the slip yoke bore to facilitate relatively smooth axial translation between the splined shaft and the slip yoke. The ends of the slip yoke bore are typically closed to maintain the lubricant within the bore and to prevent dust and other undesirable contaminants from entering the bore.
To close the open end of the yoke bore, slip spline assemblies are commonly provided with dust covers. Various connections and retaining mechanisms have been employed to retain the dust cover in the yoke bore end. When lubricant pressure excessively builds-up in the yoke bore due to sudden axial translations between the shaft and the yoke, it is desirable that the dust cover operate as a mechanical fuse and selectively fail to release the pressure build-up. Otherwise, excessive pressure build-up can impede movement between the shaft and yoke and result in damage to components either within the slip spline assembly or other external drive components associated with the input and output of the slip spline assembly.
Some of the attempts of retaining a dust cover include staking the dust cover with set screws to the yoke or welding the dust cover over the yoke bore. However, assembly of these connections have the drawback of being labor intensive. Moreover, replacement dust covers are not easily secured to the yoke bore after failure of the original dust cover. In particular, for the set screw retaining mechanism, the threads can become stripped which could require re-tapping or a completely new yoke. For the weld retaining mechanism, re-welding a replacement dust cover can cause strength problems in the yoke. FIG. 1 illustrates another prior attempt of closing the end 3 of a yoke bore 4 with a dust cover assembly 5. As illustrated in FIG. 1, the dust cover assembly 5 includes a cup shaped dust cover 6, a snap ring 7 and a resilient O-ring gasket 8. The dust cup 6 is stamped from sheet steel to provide an integral radially outward extending flange 9 that is retained by the snap ring fitted in groove 10 in the yolk bore end 3. The flange 9 also compresses the O-ring gasket 8 inserted in a second groove 11 in the yoke and forms a line seal.
A problem existing in the art is that these and other prior dust cover attempts have not achieved the sufficient failure reliability for many applications. In particular, prior dust covers that are mass produced do not fail or pop off at sufficiently consistent pressures in the yoke bore. Moreover, there has not beep a sufficiently reliable way to predict what pressure in the yoke bore will cause the dust cover to pop off. Prediction inaccuracies are amplified when the size and configuration of the dust cover are modified for the many different sizes and configurations of slip spline assemblies. This problem is further complicated by the fact that different applications using the same size and design of slip spline assembly may require different failure pressures in the yoke bore to pop the dust cover. Another drawback that sometimes occurs with some dust cover designs is that they rattle against the yoke due to vibrations in the yoke during operation of the slip spline assembly which in turn causes an undesirable noise.